<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<script>
    var a=1
    console.log(a)
    var b=3.14
    console.log(b)
    var c="hello world"
    console.log(c)
    var d=true
    console.log(d)
    a=5.5
    console.log(a)
    var a="哈哈哈哈我又来了"
    console.log(a)

    let x=1;
    console.log(x);
    x=5.5;
    console.log(x);
    let x="哈哈哈我又来了"
    // console.log(x);//报错：用let关键字声明的变量在同一个作用域下不能被重复声明

    const PI=3.14;
    console.log(PI);
    // PI=5.5; //报错：常量不能被重新赋值
</script>
</body>
</html>